What rotating device did Leonardo da Vinci sketch as a possible aerial machine?

Leonardo da Vinci sketched an aerial screw as a possible machine for rising into the air.

The design appears in a manuscript page dated to about 1489. It shows a large helical structure made from reed, linen, and wire, with a platform and people turning a central mechanism. Leonardo wrote that if the screw-shaped surface were tightly wound and rotated quickly, it might ascend by pressing against the air.

The aerial screw is often described as a forerunner of the helicopter, but that comparison needs care. Leonardo did not provide a workable modern rotor system, and human muscle power would not have been sufficient to lift the proposed structure and its crew. The sketch also lacks the detailed aerodynamic analysis and control arrangements required for practical flight.

Nevertheless, the drawing is historically important because it expresses the idea of vertical lift through a rotating helical surface. Centuries later, helicopter engineers developed powered rotors that achieved controlled vertical flight using very different materials, engines, and aerodynamic principles.